<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="f(1)">
<input type="button" value="减" onclick="f(2)">
<input type="button" value="乘" onclick="f(3)">
<input type="button" value="除" onclick="f(4)">
<div>
    结果:<span></span>
</div>

<script>
    function f(x) {
        let i1 = document.querySelector("#i1");
        let i2 = document.querySelector("#i2");
        let sum = document.querySelector("span");
        if(isNaN(i1.value) || isNaN(i2.value)){
            sum.innerText="输入有误!";
            return;
        }
        switch (x){
            case 1:
                sum.innerText= i1.value*1+i2.value*1;
                break;
                case 2:
                    sum.innerText=i1.value-i2.value;
                    break;
                    case 3:
                        sum.innerText=i1.value*i2.value;
                        break;
                        case 4 :
                            sum.innerText=i1.value/i2.value;

        }
    }


    /*function fJa() {
        let i1=document.querySelector("#i1");
        let i2 =document.querySelector("#i2");
        let sum = document.querySelector("span");
        //判断是否是数字
        if(isNaN(i1.value) || isNaN(i2.value)){
            sum.innerText="输入有误!";
            return;
        }
        sum.innerText= parseFloat(i1.value)+parseFloat(i2.value);
    }
    function fJn() {
        let i1=document.querySelector("#i1");
        let i2 =document.querySelector("#i2");
        let sum = document.querySelector("span");
        if(isNaN(i1.value) || isNaN(i2.value)){
            sum.innerText="输入有误!";
            return;
        }
        sum.innerText= parseFloat(i1.value)-parseFloat(i2.value);
    }
    function fCg() {
        let i1=document.querySelector("#i1");
        let i2 =document.querySelector("#i2");
        let sum = document.querySelector("span");
        if(isNaN(i1.value) || isNaN(i2.value)){
            sum.innerText="输入有误!";
            return;
        }
        sum.innerText= parseFloat(i1.value)*parseFloat(i2.value);
    }
    function fCu() {
        let i1=document.querySelector("#i1");
        let i2 =document.querySelector("#i2");
        let sum = document.querySelector("span");
        if(isNaN(i1.value) || isNaN(i2.value)){
            sum.innerText="输入有误!";
            return;
        }
        sum.innerText= parseFloat(i1.value)/parseFloat(i2.value);
    }*/
</script>
</body>
</html>